Wednesday, April 23, 2014
Composition of Catalytic Converters
Catalytic converters chemically change toxic car emissions into relatively harmless substances like water vapor and carbon dioxide. The U.S. Environmental Protection Agency required the devices on all new cars in the United States in 1975. Since then, the converters have prevented millions of tons of harmful carbon monoxide, unburned hydrocarbons and nitrogen oxides from turning into air pollution, according to an industry group, CatalyticConverter.org.
Catalysts
A catalyst is a material that starts or speeds up a chemical reaction. Catalytic converters use combinations of precious metals as catalysts to transform toxic gases in engine exhaust. Platinum and rhodium cause nitrogen oxides to separate into harmless oxygen and nitrogen. Platinum and palladium help oxidize carbon monoxide and unburned hydrocarbons. The metals used as catalysts are valuable. About half of all converters are recycled to reclaim their catalyst metals.
Housing and Core
Converters usually have a stainless steel outer shell coated with a thin layer of aluminum. The inner core is often made of a ceramic honeycomb coated with an extremely thin layer of the catalyst material. A honeycomb structure is used to maximize the catalyst surface area that the exhaust gases contact.
Emission Control
Sensors monitor exhaust emissions before and after they go through the converter and relay the information to an emission-control system. The control system uses data on oxygen levels to adjust the vehicles fuel injection, maintaining the air-to-fuel mix needed for the converter to operate at maximum efficiency.
